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Štefan Olejník Institute of Physics, Slovak Academy of Sciences, Bratislava, Slovakia Tübingen, November 18, Confinement problem in QCD The problem remains unsolved and lucrative: The phenomenon attributed to field configurations with non-trivial topology: Instantons? Merons? Abelian monopoles? Center vortices? Their role can be (and has been) investigated in lattice simulations.

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Štefan Olejník Institute of Physics, Slovak Academy of Sciences, Bratislava, Slovakia Tübingen, November 18, Why Coulomb gauge? Two features of confinement: Long-range confining force between coloured quarks. Absence of gluons in the particle spectrum. Requirements on the gluon propagator at zero momentum: A strong singularity as a manifestation of the long-range force. Strongly suppressed because there are no massless gluons. Difficult to reach simultaneously in covariant gauges! In the Coulomb gauge: Long-range force due to instantaneous static colour- Coulomb field. The propagator of transverse, would-be physical gluons suppressed.

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Štefan Olejník Institute of Physics, Slovak Academy of Sciences, Bratislava, Slovakia Tübingen, November 18, Center symmetry and confinement Different phases of a stat. system are often characterized by the broken or unbroken realization of some global symmetry. Polyakov loop not invariant: On a finite lattice, below or above the transition, =0, but:

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Štefan Olejník Institute of Physics, Slovak Academy of Sciences, Bratislava, Slovakia Tübingen, November 18, Coulomb energy and remnant symmetry Maximizing R does not fix the gauge completely: Under these transformations: Both L and Tr[L] are non-invariant, their expectation values must vanish in the unbroken symmetry regime. The confining phase is therefore a phase of unbroken remnant gauge symmetry; i.e. unbroken remnant symmetry is a necessary condition for confinement.

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Štefan Olejník Institute of Physics, Slovak Academy of Sciences, Bratislava, Slovakia Tübingen, November 18, Center vortices and Coulomb energy Center vortices are identified by fixing to an adjoint gauge, and then projecting link variables to the Z N subgroup of SU(N). The excitations of the projected theory are known as P-vortices. Direct maximal center gauge: Vortex removal: What happens when “vortex-removed” configurations are brought to the Coulomb gauge? Coulomb energy

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Štefan Olejník Institute of Physics, Slovak Academy of Sciences, Bratislava, Slovakia Tübingen, November 18, SU(2) in the deconfined phase: an explanation (?) Spacelike links are a confining ensemble even in the deconfinement phase: spacelike Wilson loops have an area law behaviour. Removing vortices removes the rise of the Coulomb potential. Thin vortices lie on the Gribov horizon! (A proof: D. Zwanziger.)

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Štefan Olejník Institute of Physics, Slovak Academy of Sciences, Bratislava, Slovakia Tübingen, November 18, Conclusions The Coulomb string tension much larger than the true asymptotic string tension. Confining property of the color Coulomb potential is tied to the unbroken realization of the remnant gauge symmetry in CG. The deconfined phase in pure GT, and the “confinement” region of gauge-fundamental Higgs theory: color Coulomb potential is asymptotically linear, even though the static quark potential is screened. Center symmetry breaking, spontaneous or explicit, does not necessarily imply remnant symmetry breaking. Strong correlation between the presence of center vortices and the existence of a confining Coulomb potential. Thin center vortices lie on the Gribov horizon. The transition between regions of broken/unbroken remnant symmetry: percolation transition (Kertész line).